The present invention relates to control of a system, machine or process that is repetitive in nature or is amenable to at least some degree of rehearsal. More particularly, the present invention relates to determining a repeatable control bandwidth of a vibration system, to or within a metric appropriate for the application.
Vibration systems that are capable of simulating loads and/or motions applied to test specimens are generally known. Vibration systems are widely used for performance evaluation, durability tests, and various other purposes as they are highly effective in the development of products. For instance, it is quite common in the development of automobiles, motorcycles, or the like, to subject the vehicle or a substructure thereof to a laboratory environment that simulates operating environments such as a road or test track. Physical simulation in the laboratory involves a well-known method of data acquisition and analysis in order to develop drive signals that can be applied to the vibration system to reproduce the operating environment. This method includes instrumenting the vehicle with transducers xe2x80x9cremotexe2x80x9d to the physical inputs of the operating environment. Common remote transducers include, but are not limited to, strain gauges, accelerometers, and displacement sensors, which implicitly define the operating environment of interest. The vehicle is then driven in the same operating environment, while remote transducer responses (internal loads and/or motions) are recorded to represent the xe2x80x9cdesiredxe2x80x9d response for the simulation. During simulation with the vehicle mounted to the vibration system, actuators of the vibration system are driven so as to reproduce the recorded remote transducer responses on the vehicle in the laboratory thereby replicating the desired response.
However, before simulated testing can occur, the relationship between the input drive signals to the vibration system and the responses of the remote transducers must be characterized in the laboratory. Typically, this xe2x80x9csystem identificationxe2x80x9d procedure involves obtaining a respective system model or transfer function of the complete physical system (e.g. vibration system, test specimen, and remote transducers) hereinafter referred to as the xe2x80x9cphysical systemxe2x80x9d. The inverse of the system model is used to iteratively obtain suitable drive signals for the vibration system to achieve substantially the same response from the remote transducers on the test specimen in the laboratory situation as was found in the operating environment. The iterative process can involve, for example, various methods of adjusting the drive signals iteratively until the response achieved from the physical system is acceptably close to the desired response.
As those skilled in the art would appreciate, this process of obtaining suitable drive signals is not altered when the remote transducers are not physically remote from the test system inputs (e.g. the case where xe2x80x9cremotexe2x80x9d transducers are the feedback variables, such as force or motion, of the vibration system controller).
Although the above-described system and method for obtaining drive signals for a vibration system has enjoyed substantial success, there is a continuing need to improve such systems. For example, a fundamental limitation on the accuracy with which the desired operating responses can be reproduced in the simulation test is the repeatability of the response of the physical system, as measured by the remote transducers, to the same input drive signal (repeated). Frequently, physical systems are only repeatably controllable to within an appropriate metric of accuracy over a limited frequency range. This limited frequency range, referred to herein as a xe2x80x9crepeatable bandwidthxe2x80x9d, is the frequency range over which the system can be controlled with some desired or necessary measure of repeatability. While the physical system will generally be controllable over larger frequency ranges, physical system characteristics result in repeatability exceeding the desired metric outside of the repeatable bandwidth. As discussed, one of the primary difficulties in performing laboratory simulation is to determine the frequency range over which the simulation may be expected to be repeatably accurate. A common method of predicting a simulation range is to use ordinary, partial and multiple coherences whose results often do not correlate with the results obtained during the iterative process. Moreover, coherence measurements frequently do not provide any recourse for improving the simulation bandwidth.
Commonly, when developing drive signals for the physical system, an assumption is made that the system will be used, and is repeatably controllable, over a particular frequency range. Considerable effort may be expended trying to achieve a drive signal that accurately reproduces the desired response over a frequency range that in fact may not be possible. Consequently, there is a need to accurately estimate the repeatable bandwidth of the physical system prior to modeling and/or iteratively obtaining drive signals during the system identification phase.
A system and method for identifying characteristics of a physical system applies substantially identical drive ensembles to the physical system and obtains corresponding responses from the physical system. A repeatable bandwidth of the physical system is estimated as a function of the applied drive ensembles and the corresponding obtained responses. Instructions can be provided on a computer readable medium to perform the method.